Removal of CMP residue from semiconductor substrate using supercritical carbon dioxide process

ABSTRACT

A method of removing Chemical Mechanical Polishing (CMP) residue from a semiconductor substrate is disclosed. The semiconductor substrate with the CMP residue on a surface is placed within a pressure chamber. The pressure chamber is then pressurized. Supercritical carbon dioxide and a solvent are introduced into the pressure chamber. The supercritical carbon dioxide and the chemical are maintained in contact with the semiconductor substrate until the CMP residue is removed from the semiconductor substrate. The pressure chamber is then flushed and vented.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/96,300, filed on Feb. 27, 2001, which is a continuation ofU.S. patent application Ser. No. 09/407,628, filed on Sep. 28, 1999,which claims priority from U.S. Provisional Application No. 60/101,988,filed on Sep. 28, 1998, all of which are incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of removing ChemicalMechanical Polishing (CMP) residue from semiconductor wafers. Moreparticularly, the present invention relates to the field of removing CMPresidue from semiconductor wafers using supercritical carbon dioxide.

BACKGROUND OF THE INVENTION

[0003] Manufacture of semiconductor devices commonly employ a ChemicalMechanical Polishing (CMP) process to planarize a wafer surface. The CMPprocess removes top surface layers from a semiconductor wafer. The CMPprocess leaves a CMP residue of CMP chemicals and particles that isdifficult and problematic to remove by current post-CMP cleaningmethods. It is well known that the CMP residue predominantly remains insurface features on the wafer surface.

[0004] The current post-CMP cleaning methods require that the wafersurface be mechanically washed or brushed by a commercially availablemachine called a scrubber. The scrubber may employ heat or ultrasonicaugmentation and typically requires immersion times of two to twentyminutes to achieve complete removal of the CMP residue from the wafersurface. Because the wafer surface is mechanically washed or brushed bythe scrubber, the scrubber leaves defects or scratches in the wafersurface.

[0005] It is well known that, if some of the CMP residue remains in thesurface features, performance of the semiconductor devices will bedegraded. Additionally, it is well known that the cost of manufacturinga wafer of the semiconductor devices is proportional to the timeemployed for each processing step.

[0006] It would be advantageous to be able to remove the CMP residuewithout using the mechanical washing or brushing employed by thescrubber in order to reduce an amount of the defects and the scratches.Further, it would be advantageous to more effectively remove the CMPresidue from the surface features on the wafer surface.

[0007] What is needed is a method of removing the CMP residue that doesnot use the mechanical washing or brushing.

[0008] What is further needed is a method of removing the CMP residuethat is more effective than the mechanical washing or brushing inremoving the CMP residue from the surface features.

[0009] What is additionally needed is a method of removing the CMPresidue that is more efficient than the scrubber.

SUMMARY OF THE INVENTION

[0010] The present invention is a method of removing Chemical MechanicalPolishing (CMP) residue from a surface of a semiconductor substrate. Thesemiconductor substrate, including the CMP residue on the surface, isplaced within a pressure chamber. The pressure chamber is thenpressurized. Supercritical carbon dioxide and a solvent are introducedinto the pressure chamber. The supercritical carbon dioxide and thesolvent are maintained in contact with the semiconductor substrate untilthe CMP residue is removed from the semiconductor substrate. Thepressure chamber is then flushed and vented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a flow chart illustrating the steps of a method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] The present invention utilizes high solvency and cleaningcharacteristics of supercritical carbon dioxide to assist in a post-CMPcleaning process. In the preferred embodiment, a small amount of achemical, i.e., a solvent or a solvent mixture, is added to affect thepost-CMP cleaning process as compared to the prior art. In the presentinvention, the supercritical carbon dioxide carries a small amount ofthe chemical to a wafer surface to be cleaned and is then recycled backto a carbon dioxide compressor for reuse.

[0013] The chemical is soluble or insoluble in carbon dioxide and is notdamaging to semiconductor device materials. The high solvency andsolubilizing ability of the supercritical carbon dioxide makes thismethod fast, safe, and very quick. High turbulence at wafer surfacefeatures in conjunction with hyper-efficient mass transport of achemical co-solvent package can clean the wafer surface in less thanfive minutes. CMP residue of CMP chemicals and abrasive particles iseffectively removed without direct mechanical contact, in contrast tocurrent methods. Another advantage of the present invention is that thewafer surface contains fewer defects as compared to mechanical scrubbermethods.

[0014] The solvency of supercritical carbon dioxide increases withpressure. Diffusivity and viscosity at or above a critical point ofcarbon dioxide remains similar to that of a gas phase. Because densityabove the critical point of the carbon dioxide is nearly equal to thatof a liquid state, the supercritical carbon dioxide carries the chemicalonto the wafer surface and cleans sub-micron surface features of amodern semiconductor device. In the present invention, the supercriticalcarbon dioxide also functions to carry away the CMP residue, includingthe CMP chemicals and abrasive particles, from the sub-micron surfacefeatures of the modern semiconductor device. Thus, a small amount of thechemical mixed with the supercritical carbon dioxide performs thepost-CMP cleaning process and also cleans away any remaining unwantedchemicals and the CMP residue.

[0015] The preferred embodiment of the post-CMP cleaning process of thepresent invention is illustrated in FIG. 1. The semiconductor waferincluding the CMP residue is placed in a pressure chamber in a firstprocess step 20. The pressure chamber is then sealed and pressurizedwith the carbon dioxide, in a second process step 22. As the pressureinside the pressure chamber builds, the carbon dioxide becomes liquidand then reaches supercritical temperature and pressure. Typicalconditions for this process range from 20 to 70° C. and 1050 and 6000psig. When the desired conditions are reached, a small amount of thechemical is introduced into a supercritical carbon dioxide stream andthus added into the pressure chamber to begin cleaning, in a thirdprocess step 24. Typical types and amounts of chemicals are: a. 0.1-15.0v/v % of isopropyl alcohol and related alcohols; b. 0.1-15.0 v/v % ofpropylene carbonate and related carbonates; c. 0.1-15.0 v/v % ofethylene glycol and related glycols; d. 0.001-5.0 v/v % of ozone; e.0.1-15.0 v/v % of hydrogen fluoride and related fluorides; f. 0.1-15.0v/v % of ammonium hydroxide and related hydroxides; g. 0.1-15.0 v/v % ofcitric acid and related acids; and h. 0.1-15.0 v/v % of a mixture of anyof the above chemicals.

[0016] The chemical is preferably selected from a preferred groupincluding the isopropyl alcohol, the propylene carbonate, the ethyleneglycol, the ozone, the hydrogen fluoride, the ammonium hydroxide, andthe citric acid, or a mixture thereof.

[0017] The chemical is alternatively selected from an alternative groupincluding the alcohols related to the isopropyl alcohol, the carbonatesrelated to the propylene carbonate, the glycols related to the ethyleneglycol, the fluorides related to the hydrogen fluoride, the hydroxidesrelated to the ammonium hydroxide, and the acids related to the citricacid, or a mixture selected from these chemicals and the preferredgroup.

[0018] The post-CMP cleaning process continues with recirculation of thesupercritical carbon dioxide and with mixing, i.e., agitating, thereofinside the pressure chamber until the CMP residue is removed, typicallyfrom one-half to five minutes, in a fourth process step 26. The pressurechamber is then flushed with pure supercritical carbon dioxide or liquidcarbon dioxide to remove all traces of any remaining chemicals, in afifth process step 28. Finally, the chamber is vented to atmosphere andthe wafer is removed, in a sixth process step 30. At this point, anoptional rinse in DI (deionized) or ultra pure water may be performed tofinish the cleaning process.

[0019] The present invention uses the supercritical carbon dioxide incombination with the small amount of a chemical admixture to remove theCMP residue from the surfaces of the semiconductor devices in a post-CMPcleaning system. The post-CMP cleaning system includes a wafer processchamber, a pump, a sensor system, a pressure and flow regulating system,and a recovery chamber. The wafer process chamber holds thesemiconductor wafer or semiconductor wafers. The pump is capable ofcompressing liquid carbon dioxide beyond the critical point. The sensorsystem measures temperature, pressure and flows. The pressure and flowregulating system connects a carbon dioxide source to the wafer chamberat the desired conditions. The recovery chamber collects solid andliquid material exhausted from the wafer chamber.

[0020] The post-CMP cleaning system preferably includes a temperaturecontrol system for heating the wafer process chamber.

[0021] The post-CMP cleaning system preferably includes a chemicalintroduction system for adding precise amounts of the chemical into thesupercritical carbon dioxide process stream.

[0022] The post-CMP cleaning process of the present invention includesthe following steps. The wafer is placed in the wafer process chamber.The post-CMP cleaning system is preferably purged with inert gas or thecarbon dioxide. Alternatively, the post-CMP cleaning system is notpurged. Next, the post-CMP cleaning system is pressurized with thecarbon dioxide to achieve supercritical conditions. A desired amount ofthe chemical is added into the carbon dioxide, which forms chemicalladen supercritical carbon dioxide. The chemical-laden supercriticalcarbon dioxide is contacted with the wafer. The wafer process chamber ispreferably flushed using the supercritical carbon dioxide to removecontaminants. Alternatively, the wafer process chamber is flushed usingthe liquid carbon dioxide. The post CMP cleaning system is thendepressurized to allow removal of the wafer.

[0023] The post-CMP cleaning process results in the wafer surface havinga defect level that is much lower than current cleaning methods, whichutilize mechanical contact of the wafer with roller or brush equipment.

[0024] The post-CMP cleaning process removes the CMP residue fromsemiconductors, bare silicon wafers, metallic covered wafers, and memorystorage devices. It will be readily apparent to one of ordinary skill inthe art that the post-CMP cleaning process removes the CMP residue fromother substrates, including other semiconductor substrates, that havebeen polished or planarized in the CMP process.

[0025] It will be readily apparent to one skilled in the art that othervarious modifications may be made to the preferred embodiment withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

We claim:
 1. A method of removing a chemical mechanical polishingresidue from a surface of a substrate comprising the steps of: a.placing the substrate, with the chemical mechanical polishing residue onthe surface of the substrate, within a pressure chamber; b. pressurizingthe pressure chamber; c. introducing supercritical carbon dioxide and asolvent into the pressure chamber, wherein the solvent is selected fromthe group consisting of alcohols, carbonates, glycols, ozone, fluorides,hydroxides, acids, and a mixture thereof; d. agitating the supercriticalcarbon dioxide and the solvent within the pressure chamber until thechemical mechanical polishing residue is removed from the semiconductorsubstrate; and e. flushing the pressure chamber.
 2. A method of removinga chemical mechanical polishing residue from a surface of a substratecomprising the steps of: a. placing the substrate, with the chemicalmechanical polishing residue on the surface of the substrate, within apressure chamber; b. pressurizing the pressure chamber; c. introducingsupercritical carbon dioxide and a solvent into the pressure chamber,wherein the solvent is selected from the group consisting of isopropylalcohol, propylene carbonate, ethylene glycol, ozone, hydrogen fluoride,ammonium hydroxide, citric acid, and a mixture thereof; d. agitating thesupercritical carbon dioxide and the solvent within the pressure chamberuntil the chemical mechanical polishing residue is removed from thesemiconductor substrate; and e. flushing the pressure chamber.
 3. Amethod of removing a chemical mechanical polishing residue from asurface of a substrate comprising the steps of: a. placing thesubstrate, with the chemical mechanical polishing residue on the surfaceof the substrate, within a pressure chamber; b. pressurizing thepressure chamber; c. introducing supercritical carbon dioxide and asolvent into the pressure chamber, wherein a volume ratio of the solventto the supercritical carbon dioxide is within the range and including0.001 and 15.0 percent; d. agitating the supercritical carbon dioxideand the solvent within the pressure chamber until the chemicalmechanical polishing residue is removed from the semiconductorsubstrate; and e. flushing the pressure chamber.